Note: Descriptions are shown in the official language in which they were submitted.
1(~8'~494
1 The present invention relates to a gamma prime
strengthened nickel base alloy.
United States Patent No. 3,667,938 claims an alloy
consisting essentially of, by weight, from 12.0 to 20.0% chro-
mium, from 5 to 7% titanium, from 1.3 to 3.0% aluminum, from
13.0 to 19.0% cobalt, from 2.0 to 3.5~ molybdenum, from 0.5 to
2.5% tungsten, from 0.005 to 0.03~ boron, from 0.05 to 0.15%
carbon, balance essentially nickel. Although the alloy has
good hot corrosion resistance, strength, creep resistance, phase
stability, and most importantly, stress rupture life; its hot
impact strength deteriorates at an undesirahle rate after long
ti=e service at elevated temperatures.
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iO8'~494
1 The applicant's Belgian Patent 844,246 which issued
January 11, 1977 describes an alloy having properties similar
to that of United States Patent No. 3,667,938, and yet one of
improved hot impact strength. The improvement is attained by
lowering the carbon content of 3,667,938 from a minimum value of
0.05~ to a maximum value of 0.045~. Unfortunately, lowering of
the carbon content is accompanied by some deterioration in the
stress rupture life and hot ductility of the alloy.
Through the present invention there is no~ provided
an alloy with the basic properties of the alloy described in
Belgian Patent 844,246, and yet one of improved hot ductility
and stress rupture life. Improved properties are attained
through carefully controlled additions of boron. Unlike the
alloys of United States Patent No. 3,667,938 and Belgian Patent
844,246, the alloy of the present invention contains from 0.031
I to 0.048% boron.
Other alloys with some similarities to the present
invention are disclosed in United States Patent Nos. 2,975,051,
3,385,698 and Re; 28,671. Among other differences, they do not
disclose the critical boron content of the subject invention.
Likewise, said boron content is not disclosed in the foreign
counterparts of Patent No. 3,667,938. The counterparts, which
differ somewhat from the United States patent, are discussed
in greater detail in heretofore referred to Belgian Patent
844,246.
It is accordingly an object of the present invention
to provide a gamma prime strengthened nickel base alloy.
The foregoing and other objects of the invention will
be best understood from the following description, reference
being had to the accompanying Figure which shows how stress
108'~4~4
1 rupture life varies with boron and carbon contents.
The alloy of the present invention is a gamma prime
strengthened nickel base ~lloy characterized by good hot corrosion
resistance, strength, creep resistance, phase stability and stress
rupture life. It consists essentially of, by weight, from 12.0 to
20.0~ chromium, from 4.Q to 7.0% titanium, from 1.2 to 3.5% aluminum,
from 12.0 to 2~.~% co~a~t, from 2.0 to 4.0% molybdenum, from 0.5 to
2.5~ tungsten, from ~.~31 to ~.048~ bo~on, from 0.005 to 0.15% carbon,
up to 0.75% mangaDese, ~p to 0.5% silicon, up to 1.5% hafnium, up to
~ zirconium, up to 1.0% ~preferably less than 0.5%) iron, up to
0.2% of rare e~r~h e~ements that will not lower the incipient
melting temperature ~elGw t~e solvus temperature of the gamma prime
present in ths alloy, up to 0.1% of elements from the group consisting
of magnesium, ca~cium, strontium and barium, up to 6.0~ of elements
from the group consisting of rhenium and ruthenium, balance
i essentially nickel. Exemplary rare earth elements are cerium and
lanthanum. The alloy i8 substantially free of deleterious acicular,
~igma and mu phases. Although its predominant use is in the wrought
form, it can be used in the cast or powder form.
In addition to the above, a titanium to aluminum ratio of
from 1.75:1 to 3.5:1 is imposed upon the subject alloy to help
insure the formation of spheroidal gamma prime. Gamma prime which
is believed to have the general compos~ion M3 (Al, Ti) gives the
alloy it3 strength. Of the various forms of gamma prime, spheroidal
gamma prime is preferred. As used herein the M portion of the
gamma prime compos~ion is regarded as consisting mainly of nickel
~ with some substitution of chromium and molybdenum in the approximate
;'~ proportions, 95 nickel, 3 chromium and 2 molybdenum. Respective
minimum aluminum and titanium contents of 1.2% and 4.0% are required
to insure adequate strength. For the same reason the total aluminum
.
108;~494
1 and titanium content must be at least 6.0~. The total aluminum
and titanium content should not, however, exceed 9.0% as too
much can hinder workability.
Boron, a critical element in the subject alloy, must
be present in an amount of from 0.031 to 0.048%. Stress rupture
life deteriorates at a fairly rapid rate at boron levels below
0.031~; and at levels above 0.048%, the alloy is plagued by the
onset of deleterious incipient melting, and in turn the
deterioration of stress rupture life and other porperties.
Incipient melting produces voids that, in turn, lower stress
rupture life. Moreover, excessive boron can induce at normal
regions of complex eutectics, boride-rich areas in large ingots;
which areas can cause cracking on cooling of the ingot. Therefore,
the effect of boron on stress rupture lives, as depicted in the
Figure, is most significant. Contour lines shown thereon outline
regions where certain stress rupture lives can be expected. For
example, an alloy having 0.03 wt.% carbon and 0.040% boron could
be expected to have an 1800F/16 ksi stress rupture life of at
least 120 hours. Preferred levels of boron are from 0.032 to
0.045%.
! As di closed in heretofore referred to Belgian Patent
844,246, the carbon content of the subject alloy is preferably-
maintained at a maximum level of 0.045%, and preferably below
0.04%, as impact strength has been found to deteriorate at higher
levels. Minimum and minimum preferred carbon levels are respec-
, tively O.OOS and 0.01%. A small but finite amount of carbon
~ is necessary to improve hot ductility in the working temperature
; range and to provide the desired creep resistance at temperatures
above about 1500F.
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108;~494
1 For the best combination of stress rupture life and
impact strength, the alloy of the subject invention preferably has
a carbon and boron ccntent wi~hin Area ABCD of the Figure. Area
; ABCD is defined by a carbon content of from 0.02 to 0.04% and a
boron content of from ~.032 to 0.045~. Alloys wit~in said area
- could be expected to have a 1650F impact strength of at least about
6 ft.-lbs. a~ter 35,000 hours exposure at 1600F and an 1800F/
16 ksi stress rupture life of at least 120 hours.
To provi~e the alloy with even better stress rupture
properties, ad~itions of smal1 amounts of zirconium and/or rare
earth metals can be ma~e. Rare earth additions are generally in
amounts of from 0.012 to 0.024~. Zirconium additions are generally
in amounts of fr ~.315 to 0.05%. Preferred zirconium levels are
from 0.02 to 0.035%. Zirconium levels in excess of 0.1% are
undesirable as excess zirconium may cause segregation of undesirable
phases which, in turn, result in ingot cracking and/or decreased
hot workab~iity.
1 The following examples are illustrative of several aspects
3 of the invention.
~ 20 Example ~
1 Eight nickel base alloys (Alloys A through H) were heat
~l treated as follows:
`~ 2135F - 4 hours - air cool
1975F - 4 hours - air cool
15~0F - 24 hours- air cool
¦~ ; 1400F - 16 hours- air cool
` and tested for stress rupture life at a temperature of 1800F and
~ -a stress of 16 ks~. The aim chemistry of the alloys is as follows:
.~
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108;~494
1 Cr _ Al Co Mo ~ C B Ni
18.0 5.00 2.50 14.7 3.0 1.25 * * Bal.
*varied
Carbon and boron contents for the alloys appear hereinbelow in
S Table I.
TABLE I
: Carbon Boron
Alloy (wt. %) (wt. %)
A 0.007 0.016
B - 0.014 0.034
C 0.015 0.031
D 0.020 0.048
E 0.020 0.062
.
F O . 019 0.084
G 0.035 0.048
0.033 0.033 ~ -
I The results of the stress rupture life test appear
I hereinbelo~ in Table II.
TABLE II
Stress Rupture Life
: Alloy (hours)
A 77.2
B 105.5 ~.
C 119.3
D 124.7
92.9
F 88.0
G 122.3
H 107.9
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108Z494
1 The criticality of a boron content of from 0.031 to
0.048% is apparent from Tables I and II. Each alloy with a boron
content within said range had a stress rupture life in excess of
100 hours, whereas thD al'oys with higher and lower boron contents
had stress rupture lives of less than 100 hours. For comparison
purposes, it is noted that alloy A with 0.016% boron and a carbon
content of 0.0~7%, had a stress rupture life of only 77.2 hours; -
whereas alloy B with 0.034% boron and a carbon content of 0.014~,
had a stress rupture life of 105.5 hours. Moreover, it is noted
that alloy D with 0.048~ boron and a carbon content of 0.020%, had
a stress rupture life of 124.7 hours; whereas alloy E with 0.062%
boron and a carbon content of 0.020%, had a stress rupture life of
only g2.9bcurs. Alloys within the subject invention have an
1800F/t6 ksi stress rupture life of at least 100 hours.
Example II
Two additional nickel base alloys (Alloys B' and H')
were heat treated as were Alloys A through H. The alloys were
melted with the same aim chemistry as were alloys B and H, with
the exception that Alloys B' and H' had zirconium added thereto.
The carbon, boron and zirconium contents of Alloys B, B' and H and
H' appear hereinbelow in Table III.
TABLE III
Carbon Boron Zirconium
Alloy (wt.%) (wt.%) (wt.~)
- B 0-014 0.034
B' 0.009 0.035 0.03
i
0.033 0.033
; ~' 0.041 0.033 0.03
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108'~49~
1 Alloys B' and H' were teste~ for stress rupture life as
were alloys B and H. The results of the test appear hereinbelow
in Table IV, along with the results for Alloys B and H
(reproduced from Table II).
TABLE rv
Stress Rupture ~ife
Alloy _ (Hours)
B 105.5
B' 115.8
H 107.9
~' 125.0
From Table IV, it is apparent that zirconium improves the
stress rupture properties of alloys within the subject invention.
A zirconium addition of 0.03% increased the respective stress
rupture lives of Alloys B and ~ from 105.5 and 107.9 hours to
115.8 and 125.0 hours. A-~ noted hereinabove, in a specific
embodiment the subject invention has from 0.015 to 0.05% zirconium,
and preferably from 0.02 to 0.035%.
It will be apparent to those skilled in the art that the
novel principles of the invention disclosed herein in connection
with specific examples thereof will suggest various other - -
, modifications and applicationsof the same. It is accordingly
desired that in construing the breadth of the appended claims they
shall not be limited to the specific examples of the invention
! 25 described herein.
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